Gravitational Waves in Cosmic Contexts: Standard Sirens, Compact Binary Environments, and Large-Scale Structure

Abstract

Gravitational wave astronomy and large-scale structure simulations have each become central tools for studying the universe, but they are only beginning to be treated as parts of the same framework. The rapid growth of compact binary catalogs has shifted gravitational wave science from the era of first detections to population level inferences. A leading question is: what do gravitational wave sources reveal about cosmic structure, source environments, and the formation of binary black holes? This dissertation addresses this challenge by linking simulations of large-scale structure to present and future gravitational wave observations through three complementary analyses. First, halo assembly bias in the Vishnu cosmological simulation and a new method for testing and partially correcting the effects of arrested development in low-mass halo s growth are presented. By fitting early halo mass-accretion histories and extrapolating them forward, it is shown that the assembly bias signal can be reduced by roughly a factor of two, providing further evidence for assembly bias as a reason for low-mass halo truncation and suggesting a method for mitigating this effect. Second, standard-siren searches in the later parts of LIGO’s fourth observing run are examined, focusing on how dark siren cosmology is carried out in practice within the LIGO-Virgo-KAGRA Collaboration. These analyses show that current single event constraints remain broad, but also that standard siren methods already function as a practical form of cosmological inference in a regime dominated by dark sirens, incomplete galaxy catalogs, and broad localization volumes. Third, a first attempt is explored to use the hydrodynamic simulation Illustris to assess whether future gravitational wave populations can distinguish binary black hole formation channels through differences in spatial clustering bias. Together, these results argue that gravitational wave sources are best understood as populations embedded in environments connected to larger structures, and that the future of gravitational wave astrophysics lies in detecting more mergers in future detector networks and in interpreting them within the simulated and observed universe that produces them.